Method of making a silicon-containing film

ABSTRACT

A method of making hydrogenated Group IVA compounds having reduced metal-based impurities, compositions and inks including such Group IVA compounds, and methods for forming a semiconductor thin film. Thin semiconducting films prepared according to the present invention generally exhibit improved conductivity, film morphology and/or carrier mobility relative to an otherwise identical structure made by an identical process, but without the washing step. In addition, the properties of the present thin film are generally more predictable than those of films produced from similarly prepared (cyclo)silanes that have not been washed according to the present invention. The present invention advantageously provides semiconducting thin film structures having qualities suitable for use in electronics applications, such as display devices or RF ID tags, while enabling high-throughput manufacturing processes that form such thin films in seconds or minutes, rather than hours or days as with conventional photolithographic processes.

RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.13/349,838, filed Jan. 13, 2012, pending, which is a continuation ofU.S. patent application Ser. No. 12/858,327, filed Aug. 17, 2010,pending, which is a divisional of U.S. patent application Ser. No.11/934,734, filed Nov. 2, 2007, which is a divisional of U.S. patentapplication Ser. No. 10/789,317, now U.S. Pat. No. 7,498,015, filed Feb.27, 2004, each of which is incorporated herein by reference in itsentirety. This application also may be related to U.S. patentapplication Ser. No. 10/616,147, filed Jul. 8, 2003 and entitled“Compositions and Methods for Forming a Semiconducting and/orSilicon-Containing Film, and Structures Formed Therefrom”, which isincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of silanecompositions. More specifically, embodiments of the present inventionpertain to methods of forming cyclosilane compounds that are generallyliquid at ambient temperatures, compositions including such cyclosilanecompounds, methods for forming a semiconductor and/or semiconductingthin film from such cyclosilane compositions, and structures includingsuch a film.

DISCUSSION OF THE BACKGROUND

Silane compounds are conveniently produced by reduction of chlorosilaneswith Al-containing reducing agents (e.g., lithium aluminum hydride[LiAlH₄], or LAH). The silanes obtained after purification viarecondensing or vacuum distillation oftentimes contain an appreciableamount of aluminum compounds. Without intending to be bound by anyparticular theory, it is believed that the aluminum compounds present insuch recondensed or vacuum distilled silanes adversely affect theelectrical properties of thin films made from such silanes (e.g.,resistivity), and may adversely affect the physical properties ofcompositions including such silane(s) (e.g., the ability to form auniform thin layer during spin coating).

Furthermore, there is a long-felt need for a “liquid silicon”composition. Such a composition would primarily comprise silicon, wouldbe in the liquid phase at ambient temperatures (to facilitate handling,deposition and further processing), and would yield commercial qualitysemiconducting films upon subsequent heating (e.g., annealing orcuring). Better yet, the “liquid silicon” composition would bepatternable without conventional photolithography (i.e., withoutdepositing conventional photoresist materials).

SUMMARY OF THE INVENTION

This invention is directed towards the preparation of hydrogenated GroupIVA compounds (e.g., silanes) with reduced metal impurities (e.g.,lithium, sodium, aluminum, etc.). The present invention is directedtowards successfully removing aluminum impurities from silanes via awashing step (e.g., with deionized water, dilute acid or other aqueousor polar immiscible washing agent). This washing step may also reducethe amount of lithium, sodium and/or other metal-based impurities thatare soluble in the polar phase. Thus, the invention concerns a method ofmaking a hydrogenated Group IVA compound, comprising the steps of (i)reacting a reducible Group IVA compound of the formula A_(x)X_(y) with ametal hydride (e.g., a compound of the formula M¹ _(a)M² _(b)H_(c)R_(d))to form a metal-contaminated, hydrogenated Group IVA compound; and (ii)washing the metal-contaminated, hydrogenated Group IVA compound with awashing composition comprising an immiscible polar solvent todecontaminate the metal-contaminated, hydrogenated Group IVA compound(e.g., sufficiently to remove a substantial amount of the metalcontaminants). In further aspects, the invention concerns a compositioncomprising one or more (cyclic) Group IVA compounds having less than aparticular amount of certain impurities, a method of forming asemiconducting thin film from such a composition, and a thin filmstructure formed by such a method.

The present invention enables (1) the formation of silicon thin filmswith significantly reduced Al and/or alkali metal (e.g., Li) impurities,(2) improved stability of an ink containing the present silanecomposition, and (3) an improved silane deposition process. The presentinvention further advantageously provides thin film structures havingimproved physical and/or electrical properties (e.g., film roughness,conductivity, density, adhesion and/or carrier mobility), relative tostructures made from an otherwise identical process without the washingstep and/or containing a greater proportion of metal impurities. Inaddition, the properties of the thin films are generally morepredictable than those of films produced from similarly prepared(cyclo)silanes, but that have not been washed according to the presentinvention. These and other advantages of the present invention willbecome readily apparent from the detailed description of preferredembodiments below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention will be described in conjunction with thepreferred embodiments, it will be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents, which may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. For example, the term“(cyclo)silane” as used herein generally refers to a compound that maycontain one or more cyclic rings and that consists essentially of (1) achain or framework of covalently bound silicon and/or germanium atoms,and (2) hydrogen and/or deuterium atoms bound thereto. In addition, theterm “decontaminate” means to remove some, a measurable or significantamount, or substantially all of a contaminant from a composition, andthe term “(hydrogenated) elemental material” refers to a material thatconsists essentially of atoms in an elemental state bound to each other(e.g., silicon and/or germanium in essentially an oxidation state ofzero), but which may also include hydrogen atoms nonstoichiometrically,in less than a 1:1 atomic ratio (e.g., to cap or covalently bindso-called “dangling bonds” in the elemental material). However, it willbe readily apparent to one skilled in the art that the present inventionmay be practiced without these specific details. In other instances,well-known methods, procedures, components, and circuits have not beendescribed in detail so as not to unnecessarily obscure aspects of thepresent invention.

The present invention concerns a method of making hydrogenated Group IVAcompounds (e.g., silanes), comprising the steps of (i) reacting areducible Group IVA compound with a metal hydride to form ametal-contaminated, hydrogenated Group IVA compound (i.e., having one ormore metal contaminants); and (ii) washing the metal-contaminated,hydrogenated Group IVA compound with a washing composition comprising animmiscible polar solvent to decontaminate the metal-contaminated,hydrogenated Group IVA compound.

Further aspects of the invention concern (1) a composition comprisingone or more cyclic Group IVA compounds of the formula (AH_(z))_(n),where n is from 3 to 12, each A is independently Si or Ge, each of the ninstances of z is independently 1 or 2, and the composition containsless than 100 ppm of aluminum with respect to A atoms in the Group IVAcompound; (2) an ink for printing a semiconductor and/or semiconductingthin film, including the inventive composition described herein and asolvent in which the composition is soluble; and (3) a method of makinga semiconducting film, comprising the steps of depositing the presentcomposition or ink on a substrate and curing the composition to form thesemiconducting film. Curing is generally conducted under conditionssufficient to form a doped or undoped polysilane, polygermane orgermanium-substituted polysilane having a molecular weight sufficientlyhigh and/or a chemical composition sufficiently insoluble to resistsubsequent treatment with processing solvents (e.g., in subsequentcleaning and/or development steps).

A still further aspect of the invention relates to a semiconducting thinfilm structure comprising an at least partially hydrogenated, at leastpartially amorphous Group IVA element, the Group IVA element comprisingat least one of silicon and germanium, the semiconducting materialhaving less than 100 ppm of aluminum with respect to Group IVA atoms inthe thin film structure. In preferred embodiments, the structure may beformed by the present method as described herein.

The invention, in its various aspects, will be explained in greaterdetail below with regard to exemplary embodiments.

Exemplary Methods of Making a Hydrogenated Group IVA Compound

The present invention relates to a method of making hydrogenated GroupIVA compounds (e.g., silanes), comprising the steps of (i) reacting oneor more reducible (e.g., halogenated and/or alkoxylated) Group IVAcompounds with a metal hydride to form a metal-contaminated,hydrogenated Group IVA compound; and (ii) washing themetal-contaminated, hydrogenated Group IVA compound with a washingcomposition comprising an immiscible polar solvent to decontaminate themetal-contaminated, hydrogenated Group IVA compound. In variousembodiments, the halogenated and/or alkoxylated Group IVA compoundscomprise or consist essentially of compound(s) of the formulaA_(x)X_(y), where each A is independently Si or Ge, each X isindependently a halogen or an alkoxy group (e.g., a C₁-C₆ alkoxy group,a C₁-C₄ alkoxy-C₂-C₆ alkyleneoxy group, a C₆-C₁₂ aryloxy group or aC₆-C₁₀ aryl-C₁-C₄ alkyleneoxy group), x is from 3 to 12, and y is from xto (2x+2); the metal hydride comprises a compound of the formula M¹_(a)M² _(b)H_(c)R_(d), where M¹ and M² are independently first andsecond metals, each R in the metal hydride compound is independently aligand bound to at least one of M¹ and M² by a covalent, ionic orcoordination bond, at least one of a and b is at least 1, c is at least1, and d is 0 or any integer up to one less than the number of ligandbinding sites available on the (a+b) instances of M¹ and M²; and/or themetal-contaminated Group IVA compound is washed with the washingcomposition sufficiently to remove a substantial amount of the metalcontaminants. In certain implementations, x and y are selected such thatthe Group IVA compound(s) and/or hydrogenated Group IVA compound areliquid at ambient temperatures (e.g., from 15° C. to 30° C.). In otherembodiments, M¹ is at least one alkali and/or alkaline earth metal andM² is at least one of the transition metals and/or a Group IIIA (orGroup 13) element selected from the group consisting of boron, aluminum,gallium, and indium.

Where X in the compound of the formula A_(x)X_(y) is a C₁-C₆ alkoxygroup, a C₁-C₄ alkoxy-C₂-C₆ alkyleneoxy group, a C₆-C₁₂ aryloxy group ora C₆-C₁₀ aryl-C₁-C₄ alkyleneoxy group, X may be methoxy, ethoxy,n-propoxy, isopropoxy, n-butoxy, s-butoxy, t-butoxy, n-hexyloxy,s-hexyloxy, t-hexyloxy (e.g., —OCH₂CH₂C[CH₃]₃), methoxyethoxy,ethoxyethoxy, propoxyethoxy, methoxypropoxy, ethoxypropoxy,butoxybutoxy, phenoxy (—OC₆H₅), cresyl (—OC₆H₄CH₃), benzyloxy, etc.Alternatively, two X groups in the compound of the formula A_(x)X_(y)may form a C₂-C₆ alkylenedioxy group, such as ethylenedioxy (—OCH₂CH₂O—)or propylenedioxy (—OCH₂CH₂CH₂O—), or an ortho-arylenedioxy group, suchas o-(—O—)₂C₆H₄. However, in preferred embodiments, X is a halogen, suchas chloride or bromide (more preferably Cl).

More specifically, the method relates to a metal hydride reduction of aperhalo(cyclo)silane of the formula Si_(x)X_(y) to form a corresponding(cyclo)silane of the formula Si_(x)H_(y), where the (cyclo)silane issubsequently purified by washing (e.g., with an aqueous washingcomposition). The present washing step is believed to be novel and to beresponsible for the observed reductions in metal impurities. In variousembodiments, the washing composition comprises or consists essentiallyof a polar organic solvent that is immiscible with the silanecomposition (e.g. acetonitrile), deionized water, a saline solution(e.g., brine), or a dilute aqueous acid. In a preferred implementation,the washing composition consists essentially of deionized water.

However, in various alternative embodiments, the washing compositioncomprises dilute acid, which (i) has a pH of from 1 to less than 7 (andthus comprises a dilute aqueous acid), (ii) may further comprise abuffer (e.g., the composition comprises a buffered aqueous acid), and/or(iii) is selected from the group consisting of dilute aqueous HCl,dilute aqueous HBr, dilute aqueous HI, etc. Buffers, when employed, mayinclude alkaline metal, alkaline earth and ammonium salts of thecorresponding acid used in a dilute acid composition. For example, thebuffered aqueous acid may comprise dilute aqueous acetic acid bufferedwith ammonium acetate and/or an alkali metal acetate salt. Buffers mayalso include conventional buffers such as conventional sodium and/orpotassium phosphate, oxalate and/or tartrate salt buffers. Alkalinesolutions (e.g., having a pH of >9) are generally avoided, as suchsolutions may initiate and/or promote oligomerization, polymerizationand/or rearrangement of the (cyclo)silane.

The relative proportions of the contaminated hydrogenated Group IVAcompound and the washing composition may be any that effectively removemetal contaminants from the hydrogenated Group IVA compound. Forexample, the washing composition and the hydrogenated Group IVA compoundmay be present in a volume ratio of from 10:1 to 1:10 (not including anyrelatively non-polar organic solvent or other component that may bepresent in or with the hydrogenated Group IVA compound), from 5:1 to1:5, or from 3:1 to 1:1.

The present method may further comprise the step of purifying the(metal-contaminated) hydrogenated Group IVA compound, either before orafter the washing step. Such purifying typically comprises distillingthe hydrogenated Group IVA compound, optionally under reduced pressure(e.g., from 0.1 to 50 Torr) and/or at ambient temperature or higher(e.g., from about 15° C. to about 90° C., or from about 20° C. to about60° C.). For example, typical conditions for distilling cyclo-Si₅H₁₀include a temperature of about 25° C. and a pressure of about 0.5 Torr.

Prior to the present washing step, the (cyclo)silane may include metalcontaminants of up to 0.1-0.2 atom % or more (with respect to siliconand/or germanium atoms in the (cyclo)silane), particularly where the(cyclo)silane is synthesized using aluminum compounds (see thediscussion below). However, after the present washing step, the metalcontaminant(s) are typically present in a concentration or amount ofless than 100 parts per million Group IVA atoms in the (cyclo)silane,preferably less than 10 parts per million Group IVA atoms, and morepreferably less than 1 part per million Group IVA atoms. Thus thepresent washing step is capable of reducing metal contamination (andparticularly aluminum contamination) in the hydrogenated Group IVAcompound by 2, 3, 4, or more orders of magnitude.

In one example, after distillation or recondensation from ahydro-dehalogenation reaction mixture, the (cyclo)silane or(cyclo)silane mixture is washed with deionized water of pH=7 for alength of time of from about 1 to about 5 minutes. The volume ratio ofdeionized water to silane(s) is from about 5:1 to about 1:2. Afterseparation of the silane phase and drying over molecular sieves (4{acuteover (Å)}) for a length of time of from about 0.1 minutes to about 1hour, the (cyclo)silane phase is further applied as an ink onto asubstrate. The Al content was measured. Compared to a film obtained froman otherwise essentially identical, but unwashed, (cyclo)silane batch,the Al content decreased by about 4 orders of magnitude (from about 0.1at. % to about 100 ppb), as determined by secondary ion massspectroscopy (SIMS).

In a further aspect, the method further comprises the step of drying thehydrogenated Group IVA compound, after the washing step. Typically,drying comprises contacting the hydrogenated Group IVA compound with adrying agent or desiccant, such as molecular sieves, anhydrous sodium ormagnesium sulfate, anhydrous silica, etc., or exposing the hydrogenatedGroup IVA compound to a drying agent or desiccant, such as CaCl₂, CaSO₄or perhaps even P₂O₅ that is physically separated from the hydrogenatedGroup IVA compound (for example by placing the drying agent in onesection of a two-walled flask or container and the hydrogenated GroupIVA compound in the other section, then sealing the flask or containerand optionally purging the atmosphere to put the drying agent andhydrogenated Group IVA compound under a vacuum or an inert atmosphere).

The compound of the formula A_(x)X_(y) may be any straight-chain,branched, cyclic or polycyclic silane, germane, germasilane orsilagermane useful for making hydrogenated silanes for thinsemiconductor films. However, in preferred embodiments, the compound ofthe formula A_(x)X_(y) comprises a cyclic or polycyclic perhalosilane orperhalogermasilane. Thus, the resulting (cyclo)silane preferablycomprises a cyclic Group IVA compound of the formula (AH_(z))_(n), wheren is from 3 to 12, and each of the n instances of z is independently 1or 2, and in one embodiment, A is Si, n is from 4 to 8, and z is 2.Thus, the perhalosilane may be selected such that it yields such acyclosilane (or mixture of such cyclosilanes) upon hydro-dehalogenation.In one implementation, the (cyclo)silane comprises a mixture ofcompounds of the formula (AH_(z))_(n), where the majority (i.e., >50 mol%) of the (cyclo)silane composition consists of (SiH₂)₅, accompanied bysmaller molar proportions (e.g., ≦20 mol % each) of (SiH₂)₆, (SiH₂)₇and/or (SiH₂)₈. In various examples, the (cyclo)silane compositioncomprises >80 mol % (preferably >90 mol %) of (SiH₂)₅, and from 0.1 to10 mol % each (preferably from 0.5 to 5 mol %) of (SiH₂)₆, (SiH₂)₇and/or (SiH₂)₈. Typically, small amounts (e.g., <10 mol %, preferably <5mol %, more preferably <3 mol %) of n-silanes and/or iso-silanes of theformula Si_(n)H_(n+2) are present in such a mixture, where n is from 4to 10 in such n-silanes and iso-silanes. The (cyclo)silane compositionmay further contain one or more high molecular weight silanes having,e.g., 60 or more silicon atoms therein. Such higher molecular weightsilanes, which may form in a greater amount or proportion the longer thepresent washing and/or drying steps are conducted, tend to increase theviscosity of the (cyclo)silane composition, thereby improving itsproperties for certain applications (e.g., inkjetting, spin coating,curing, etc.).

Of course, the present method also comprises a metal hydride reduction(or hydro-dehalogenation) of a reducible (cyclo)perhalosilane (e.g., ofthe formula A_(x)X_(y)) to form the hydrogenated Group IVA compound(e.g., of the formula (AH_(z))_(n)). Generally, the metal hydride isadded to a solution of A_(x)X_(y) at a temperature of from −78° C. toabout 200° C. (preferably from about −20° C. to about 100° C., morepreferably from about −10° C. to about 30° C.), depending on the solventand the reactivities of the A_(x)X_(y) compound(s) and the metalhydride, then the reaction mixture is stirred until the reaction issubstantially complete. In various embodiments (except where the metalhydride is generated in situ using a catalytic amount of a metal hydrideprecursor), a solution of the metal hydride may be added to a solutionof A_(x)X_(y) over a period of time of from 1 minute to 10 hours, 5minutes to 4 hours, or 10 minutes to 2 hours, and/or at a rate of from 1to 100 mmol of metal hydride/minute, 3 to 50 mmol/minute, or 5 to 25mmol/minute. In one implementation (on a scale of about 10 grams of[cyclo]silane), a solution of metal hydride is added over about an hourat a rate of about 8-10 mmol/minute. The reaction may be monitored(e.g., by infrared or FT-IR spectroscopy, gas phase chromatography, ¹Hor ²⁹Si NMR spectroscopy, etc.), and if necessary and/or desired, warmed(e.g., from ≦0° C. to ambient temperature, or from ambient temperatureto 50-100° C., etc.) until the reaction is complete. This total reactiontime may be from 10 minutes to 2 days, 1 to 24 hours, or 4 to 16 hours.The molar ratio of hydrogen atoms in the metal hydride to X groups(e.g., halogen atoms) in the (cyclo)silane can be from 5:1 to about 1:1,and is preferably about 2:1 (e.g., from about 1.9:1 to about 2.1:1).

Exemplary solvents for the metal hydride reduction reaction includealkanes (e.g., C₅-C₁₂ branched or unbranched alkanes and cycloalkanes),fluorinated alkanes (e.g., C₃-C₈ alkanes having from 1 to 2n+2 fluorinesubstituents and C₃-C₆ cycloalkanes having from 1 to 2n fluorinesubstituents, where n is the number of carbon atoms), arenes (e.g.,benzene), substituted arenes (e.g., N-methylpyrrole or C₆-C₁₀ areneshaving from 1 to 8 fluorine substituents and/or C₁-C₄ alkyl and/oralkoxy substituents; preferably benzenes having from 1 to 6 fluorine,C₁-C₂ alkyl and/or methoxy substituents), aliphatic ethers (e.g., ethershaving two C₂-C₆ branched or unbranched alkyl groups, or 1 methyl groupand one C₄-C₆ branched or unbranched alkyl group), cyclic ethers (e.g.,tetrahydrofuran or dioxane), and glycol ethers (e.g., of the formula(CH₃(CH₂)_(w))O((CH₂)_(x)O)_(y)(CH₂)_(z)CH₃), where x is independently2-4 [preferably 2], y is 1-4 [preferably 1 or 2], and w and z areindependently 0 to 3 [preferably 0]). The solvent selected fordissolving the perhalo(cyclo)silane compound(s) may be the same as ordifferent from the solvent selected for dissolving the metal hydride. Apreferred solvent for dissolving the perhalo(cyclo)silane compound(s) iscyclohexane, and a preferred solvent for dissolving the metal hydride isdiethyl ether.

In the perhalo(cyclo)silane compound subject to metal hydride reductionwhere X is a halogen, X may be selected from the group consisting of Cl,Br and I, but is preferably Cl. Also, the perhalo(cyclo)silane compoundof the formula A_(x)X_(y) may comprise a mixture ofperhalo(cyclo)silanes of the formula (AX_(z′))_(n′), where n′ and z′ areas described above for n and z, but which are independent for eachcompound in the mixture. In one example, the perhalo(cyclo)silanecomprises a mixture of compounds of the formula (SiX₂)_(n′), where thepredominant portion (i.e., >80 mol %) of the perhalo(cyclo)silanecomposition consists of (SiX₂)₅, accompanied by a smaller molarproportion (e.g., from 0.5 to 10 mol %) of (SiX₂)₄ and, typically, aneven smaller molar proportion (e.g., from 0 to <10 mol %) of (SiX₂)₆.Thus, in one embodiment, A is Si, x is from 4 to 6, and y is from 8 to12.

The metal hydride used to reduce the halogenated or alkoxylated(cyclo)silane compound may comprise a compound of the formula M¹ _(a)M²_(b)H_(c)R_(d). In certain embodiments, d is 0, and the metal hydridecomprises a compound of the formula M¹ _(a)M² _(b)H_(c); or a is 0, andthe metal hydride comprises a compound of the formula M² _(b)H_(c)R_(d).In some embodiments, M¹ may comprise an alkali or alkaline earth metal,M² comprises one or more members selected from the group consisting oftransition metals and Group IIIA elements, and a and b are each aninteger of at least one. In such embodiments, the alkali metal may beselected from the group consisting of lithium, sodium, potassium,rubidium and cesium (preferably lithium, sodium and potassium); thealkaline earth metal may be selected from the group consisting ofberyllium, magnesium, calcium, strontium and barium (preferablymagnesium and calcium); the transition metal may be selected from thegroup consisting of yttrium, lanthanum, titanium, zirconium, vanadium,niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium,iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium andplatinum (preferably titanium, zirconium, niobium, chromium, molybdenum,tungsten, rhenium, ruthenium, osmium, rhodium, iridium, palladium andplatinum); and the Group IIIA element may be selected from the groupconsisting of boron, aluminum, gallium and indium (preferably aluminum).In some embodiments, the Group IIIA element may include aluminum andboron (e.g., an aluminoborohydride).

Examples of suitable metal hydrides of the formula M¹ _(a)M² _(b)H_(c)include lithium aluminum hydride, calcium aluminum hydride, and(possibly) sodium borohydride. Examples of suitable metal hydrides ofthe formula M² _(b)H_(c)R_(d) include dialkylaluminum hydrides such asdiisobutylaluminum hydride (DIBAL). In such compounds (i.e., in which dis at least 1), R may be an alkyl group (e.g., a straight-chain orbranched C₁-C₆ alkyl group), an alkoxy group (e.g., a straight-chain orbranched C₁-C₆ alkoxy group), an alkoxyalkylene group (e.g., astraight-chain or branched C₁-C₄ alkyl-C₁-C₆ alkylene group), analkoxyalkyleneoxy group (e.g., a straight-chain or branched C₁-C₄alkoxy-C₁-C₆ alkylene group), a cyano group, etc. Examples of suitablemetal hydrides of the formula M² _(b)H_(c) include aluminum hydride,gallium hydride, and aluminum borohydride (AlB₃H₁₂). A suitable metalhydride of the formula M¹ _(a)M² _(b)H_(c)R_(d) is sodiumdihydrido-bis-(2-methoxyethoxy)aluminate. Thus, in various embodiments,(i) M² comprises a member selected from the group consisting oftransition metals and Group IIIA elements (as described above), a is 0or 1, d is at least 1, and R is an alkyl group, an alkoxy group, analkoxyalkylene group, an alkoxyalkyleneoxy group or a cyano group(preferably M² comprises aluminum, R is a C₁-C₆ alkyl group, and c and dare integers having a ratio of from 1:2 to 2:1); or (ii) a is 1 and M¹comprises an alkali metal, each R is independently a C₁-C₆ alkyl group,a C₁-C₆ alkoxy group, a C₁-C₄ alkyl-C₁-C₆ alkylene group, a C₁-C₄alkoxy-C₁-C₆ alkylene group or a C₁-C₄ alkoxy-C₁-C₆ alkyleneoxy group,and c and d are integers having a ratio of from 1:3 to 3:1.

Alternatively, the metal hydride may be generated or created in situduring catalytic hydro-dehalogenation using a transition metal catalyst.In such a case, the transition metal may be selected from thosedescribed above, and R may be selected from monodentate ligands (e.g., atrialkyl amine such as trimethyl or triethyl amine, a trialkyl phosphinesuch as trimethyl or triethyl phosphine, a triaryl phosphine such astriphenyl phosphine, CO, pyridine, CN, a halogen such as Cl, OH, an oxogroup [═O], etc.), bidentate ligands (e.g., diethers such asdimethoxyethane, diamines such as 1,2-bis(dimethylamino)ethane orbipyridine, etc.), and polydentate ligands (such as cyclopentadienyl,pentamethylcyclopentadienyl, benzene, etc.). Typically, such catalytichydro-dehalogenation are performed under a medium to high pressure ofhydrogen gas (e.g., from a few atm to many tens of atm; e.g., from 3 to100 atm, or from 5 to 50 atm), and at a temperature of from ambienttemperature (e.g., from about 15° C. to about 30° C.) to several hundreddegrees (e.g., up to 100° C., 150° C., or 200° C.).

The halogenated and/or alkoxylated (cyclo)silane compound or compositionmay be synthesized by reducing and oligomerizing a compound of theformula AR′₂X₂ (where R′ is, e.g., aryl [such as phenyl or tolyl] oralkyl [such as methyl, ethyl, propyl, isopropyl, n-butyl, s-butyl,t-butyl, cyclohexyl, etc.), followed by treating the reduced andoligomerized compound with a mixture of a Lewis acid and a hydrogenhalide, such as AlCl₃ and HCl gas (e.g., when R′ is aryl) or SbX₅-basedsystems (e.g., when R′ is alkyl), to form a corresponding Group IVAhalide compound. However, a more preferred synthetic route comprises (a)reducing and oligomerizing a compound of the formula AR′₂X₂, then (b) inone reaction vessel, first (i) treating the reduced and oligomerizedcompound of the formula A_(x′)R′_(y′), with a mixture of a Lewis acidand a hydrogen halide to form a corresponding Group IVA halide compound,then (ii) reacting the Group IVA halide compound with a metal hydride toproduce the hydrogenated Group IVA compound (e.g., of the formula(AH_(z))_(n)). Alternatively, the reduced and oligomerized compound ofthe formula A_(x′)R′_(y′), (e.g., perphenylpentasilane) may be reactedwith HX (e.g., HBr) under high pressure (e.g., in a Parr vessel) withoutusing any catalyst to form the Group IVA halide compound.

Thus, the present method may further comprise the step of reacting acompound of the formula A_(x′)R′_(y′), (e.g., A_(x′)Ar_(y′), where Ar isaryl as described above and x′ and y′ are as described above for x andy, respectively, but which may be the same as or different from x and y,respectively) with HX (in this case, where X is a halogen) and a Lewisacid compound of the formula M³ _(p)X_(q) to form a perhalo(cyclo)silane(e.g., the compound of the formula A_(x)X_(y)). In various embodiments,Ar is an aryl group which may be substituted with alkyl (e.g.,straight-chain or branched C₁-C₆ alkyl groups), alkoxy (e.g.,straight-chain or branched C₁-C₆ alkoxy groups), aryl (e.g., C₆-C₁₀ arylgroups), aralkyl (where the aryl and alkyl constituents may be asdescribed herein), halogen, dialkylamino (where the alkyl constituentsmay be as described herein) and/or nitro groups; M³ comprises a memberselected from the group consisting of transition metals and Group IIIAelements (as described above); p is 1 or 2; and/or q is any integer upto the number of ligand binding sites available on the p instances ofM³. In preferred embodiments, x′ is from 3 to 12, preferably from 4 to6; y′ is 2*x′; A is Si; Ar is phenyl; and/or X is Cl or Br, preferablyCl. In a preferred implementation, HX is HCl and the compound of theformula M³ _(p)X_(q) is AlCl₃.

In one implementation, the reaction between a compound of the formulaA_(x′)Ar_(y′), HX and a compound of the formula M³ _(p)X_(q) to form theperhalo(cyclo)silane and the subsequent hydro-dehalogenation reactionare performed consecutively in a single reaction vessel. Thus, thepresent method may further comprise adding the metal hydride to thereaction mixture containing the perhalo(cyclo)silane compound(s) (i.e.,the product(s) from the reaction between the compound of the formulaA_(x′)R′_(y′), HX and a compound of the formula M³ _(p)X_(q)), withoutisolating or purifying the perhalo(cyclo)silane compound(s) before themetal hydride addition.

The reaction to form the perhalo(cyclo)silane compound or composition isgenerally conducted under rigorously dry conditions. For example, thesolvent(s) and reagents in solid or liquid phase are generally purified,degassed and dried (in accordance with conventional techniques) prior touse. Gas phase reagents (e.g., HX gas) are generally purchased in dryform, and techniques to preserve its dryness are generally employed whentransferring the gas phase reagent(s) to the reaction vessel. Such gasphase reactants may be continuously added to the reaction vessel (e.g.,by bubbling through the reaction mixture). The reaction to form theperhalo(cyclo)silane compound or composition may be conducted at atemperature of from about −78° C. to about 200° C., from about 0° C. toabout 150° C., or from ambient temperature (e.g., from about 15° C. toabout 30° C.) to about 100° C., until the reaction is complete. As forthe hydro-dehalogenation reaction above, the reaction to form theperhalo(cyclo)silane may be monitored (e.g., by infrared or FT-IRspectroscopy, gas phase chromatography, ¹H or ¹³C or ²⁹Si NMRspectroscopy, etc.) to determine completeness. In various embodiments,the reaction may be conducted for a length of time of from 1 to 48hours, 2 to 24 hours, or 4 to 16 hours. On a scale involving aboutone-half of a mole of silicon atoms, the reaction was conducted for alength of time of from 5 to 8 hours.

Generally, the solvents suitable for dissolving the perhalo(cyclo)silanedescribed above are suitable for the reaction to form theperhalo(cyclo)silane compound(s). Typically, a catalytic amount of Lewisacid is used in this reaction. For example, the Lewis acid may bepresent in a ratio of from 1 to 200 mmol (or from 3 to 100 mmol, or from5 to 50 mmol) per mole of A atoms in the compound of the formulaA_(x′)R′_(y′). Alternatively, the Lewis acid may be present in a ratioof from 0.25 to 100 mmol (or from 1 to 50 mmol, or from 2 to 30 mmol)per mole of R′ substituents or moieties in the compound of the formulaA_(x′)R′_(y′).

A preferred method of synthesizing the compound of the formulaA_(x′)R′_(y′), (e.g., A_(x′)Ar_(y′)) comprises reacting a compound ofthe formula A_(u)R′_(v)X′_(w) with a reducing agent to form the compoundof the formula A_(x′)R′_(y′). Typically, u is at least 1, v is at least1, and w is any integer up (2u+2−v). In one implementation, A is Si, uis 1, v is 1 or 2, and w is (4−v). The reducing agent may be anyreducing agent that effectively produces A_(x′)Ar_(y′) fromA_(u)Ar_(v)X′_(w), but preferably, the reducing agent comprises analkali metal.

The reaction to form the compound of the formula A_(x′)R′_(y′) may alsobe conducted at a temperature of from about −78° C. to about 200° C.,from about −20° C. to about 150° C., or from about −5° C. to about 100°C., until the reaction is complete. In one embodiment, the startingmaterial of the formula A_(u)R′_(v)X′_(w) is added to the reactionmixture containing the reducing agent at a first, relatively lowtemperature (e.g., from about −10° C. to about 10° C.), then after thestarting material addition is complete, the reaction temperature israised to ambient temperature (e.g., from about 15° C. to about 30° C.)for a first period of time, and then (optionally) the reaction mixtureis heated to a temperature of less than about 80° C. (e.g., the refluxtemperature of a solvent having a boiling point of less than 80° C.) fora second period of time sufficient to substantially complete thereaction. As for the hydro-dehalogenation reaction above, the reactionto form the compound of the formula A_(x′)R′_(y′) may be monitored(e.g., by infrared or FT-IR spectroscopy, gas phase chromatography, ¹Hor ¹³C or ²⁹Si NMR spectroscopy, or if the reducing agent is insoluble,by visually observing its disappearance, etc.) to determinecompleteness. In various embodiments, the first period of time may befrom 15 minutes to 16 hours, 30 minutes to 12 hours, or 1 to 8 hours,the second period of time may be from 30 minutes to 48 hours, 1 to 24hours, or 2 to 12 hours, and the total reaction time may be from 1 to 48hours, 2 to 24 hours, or 4 to 16 hours. On a scale involving about onemole of silicon atoms, the reaction was conducted for a length of timeof about 6-7 hours, and on about a 4 mole scale, for about 10 hours.

Any of the solvents described above for dissolving theperhalo(cyclo)silane or metal hydride are suitable for the couplingreaction (to form A_(x′)R′_(y′) from A_(u)R′_(v)X′_(w)), except forthose that may deprotonate in the presence of the reducing agent.Preferred solvents include alkanes (e.g., C₅-C₁₂ branched or unbranchedalkanes and cycloalkanes), arenes (e.g., benzene), substituted arenes(e.g., benzenes having from 1 to 3 C₁-C₄ alkyl and/or alkoxysubstituents; preferably benzenes having 1 or 2 C₁-C₂ alkyl and/ormethoxy substituents), aliphatic ethers (e.g., ethers having two C₂-C₆branched or unbranched alkyl groups, or 1 methyl group and one C₄-C₆branched or unbranched alkyl group), cyclic ethers (e.g.,tetrahydrofuran or dioxane), and glycol ethers (e.g., of the formula(CH₃(CH₂)_(w))O((CH₂)_(x)O)_(y)(CH₂)_(z)CH₃), where x is independently2-4 [preferably 2], y is 1-4 [preferably 1 or 2], and w and z areindependently 0 to 3 [preferably 0]). A particularly preferred solventfor the coupling reaction is tetrahydrofuran (THF).

Generally, a slight molar excess of reducing agent is reacted with thestarting material of the formula A_(u)R′_(v)X′_(w) (e.g., from 1.0 to1.1 moles, and preferably from 1.001 to 1.05 moles, of reducing agentper mole of X′ atoms in the starting material). After the reaction iscomplete, a small amount (e.g., from 0.1 to 100 ml, 0.5 to 50 ml, or 1to 25 ml) of deionized and/or distilled water may be slowly andcarefully added to the reaction mixture to quench the reaction. Theresulting mixture may be poured into a relatively large amount (e.g., avolume of from 1 to 5 times the reaction mixture volume) of deionizedand/or distilled water (preferably at least deionized water), andstirred for a period of time of from 15 minutes to 8 hours, 30 minutesto 6 hours, or 1 to 4 hours. The reaction mixture phases may beseparated (e.g., by filtering if the reaction mixture includes a solidphase, or by decanting and/or use of a reparatory funnel if the reactionmixture includes more than one liquid phase), and theorganic/silicon-containing phase may be washed with water and dried(e.g., under vacuum, and/or if the product of the formula A_(x′)R′_(y′)has a sufficiently high melting point, by heating to a temperaturesignificantly below its melting point).

In addition to the process described above, compounds of the formulasA_(x′)R′_(y′), A_(x′)Ar_(y′), A_(x)X_(y) and/or (AH_(z))_(n) may be madeby conventional methods, such as those described in, e.g., U.S. Pat.Nos. 4,554,180, 4,683,145, 4,820,788, 5,942,637 and 6,503,570, and in,e.g., Kumada, J. Organomet. Chem., 100 (1975) 127-138, Ishikawa et al.,Chem. Commun., (1969) 567, Hengge et al., J. Organomet. Chem., 212(1981) 155-161, Hengge et al., Z. Anorg. Allg. Chem., 459 (1979)123-130, and Hengge et al., Monatshefte für Chem., 106 (1975) 503-512,the relevant portions of which are incorporated herein by reference.Furthermore, the methods disclosed in any one of these references may bemodified as suggested and/or disclosed in another of these references.However, the preferred method comprises reducing and oligomerizing AR′X₃and/or AR′₂X₂ (where R′ is, e.g., phenyl), followed by treating with amixture of a Lewis acid and a hydrogen halide, such as AlCl₃ and HClgas, to form a corresponding Group IVA halide compound, then reducingwith a metal hydride (such as lithium aluminum hydride) to form amixture of mainly c-(AH₂)_(x), where x is from 5 to 8, preferably 5 to6.

Exemplary Compositions

In one aspect, the present invention relates to a composition forforming semiconductor and/or semiconducting thin films, particularlypatterned semiconducting thin films, and more particularly patternedsilicon thin films. The composition generally comprises (a) at least onecyclic Group IVA compound of the formula (AH_(x))_(n), where n is from 3to 12, each of the n instances of x is 1 or 2, and each A isindependently Si or Ge, and (b) less than 100 ppm of aluminum, withrespect to the total number of A atoms in the Group IVA compound.Preferably, the cyclic Group IVA compound(s) comprise cyclosilanes.Thus, the terms “cyclic Group IVA compound(s)” and “cyclosilane(s)” maybe used somewhat interchangeably herein. In certain embodiments, thecyclosilane has the formula (AH₂)_(n), where n is from 5 to 8. Infurther preferred embodiments, the composition comprises less than 10ppm (and more preferably, less than 1 ppm) of aluminum with respect toatoms of A in the Group IVA compound.

Examples of suitable cyclic Group IVA compounds can be found in U.S.Pat. Nos. 6,541,354, 6,527,847, 6,518,087, 6,514,801, 6,503,570,5,942,637, 5,866,471 and 4,683,145, and in U.S. Patent ApplicationPublication 2003/0045632, the relevant portions of each of which areincorporated herein by reference. These compounds include c-(SiH₂)₃,c-(SiH₂)₄, c-(SiH₂)₅, c-(SiH₂)₆, c-(SiH₂)₇, c-(SiH₂)₈,tetracyclo-(SiH)₄, pentacyclo-(SiH)₆, hexacyclo-(SiH)₈, c-(SiH₂)₄(GeH₂),c-(SiH₂)₅(GeH₂), c-(SiH₂)₃(GeH₂)₂, c-(SiH₂)₄(GeH₂)₂, c-(SiH₂)₂(GeH₂)₃,c-(SiH₂)(GeH₂)₄, c-(GeH₂)₅, and mixtures thereof.

Another aspect of the invention relates to the chemical makeup of thepresent composition. For example, at least 90 mol % (preferably at least95 mol %) of the composition consists essentially of the cyclic GroupIVA compound (which may, in turn consist of a mixture of such cyclicGroup IVA compounds, as described above). In some examples, at least 98mol % of the composition consists essentially of the cyclic Group IVAcompound(s).

Exemplary Inks

In another aspect, the present invention concerns an ink for printing orotherwise forming a semiconductor and/or semiconducting thin film. Theink may comprise or consist essentially of the exemplary (cyclo)silanecomposition described above. Where the ink consists essentially of the(cyclo)silane, the (cyclo)silane may also function as a solvent forother components (such as binding agents, thickening agents,photosensitizers, semiconductor nanoparticles, etc.). Alternatively, theink may include, for example, the exemplary (cyclo)silane compositiondescribed above and a solvent in which the composition is soluble. Insuch an embodiment, the (cyclo)silane compound(s) may be present in theink in a percentage by volume of from 0.1 to 50 vol. %, from 0.5 to 30vol. %, or from 1.0 to 20 vol. %.

In further embodiments, the solvent in the present ink comprises anaprotic solvent and/or an apolar solvent. In the context of the presentinvention, an “apolar” solvent is one that may have a gas-phase dipolemoment of about 2 debyes or less, about 1 debye or less, or about 0.5debye or less. In many implementations, an apolar solvent has a dipolemoment of about 0 debyes, due to its molecular symmetry (e.g., carbontetrachloride, tetrachloroethylene, benzene, p-xylene, dioxane) and/orhighly covalent nature of the chemical bonds therein (e.g., mineralspirits, hexane, cyclohexane, toluene). In some embodiments, the presentink comprises a solvent having a boiling point of about or less than250° C., preferably about or less than 200° C., and more preferablyabout or less than 150° C., at atmospheric pressure.

Exemplary solvents for the present ink composition include alkanes(e.g., C₅-C₁₂ branched or unbranched alkanes and cycloalkanes,preferably C₆-C₁₀ cycloalkanes such as cyclooctane), halogenated alkanes(e.g., C₁-C₄ alkanes having from 1 to 2n+2 halogen substituents andC₃-C₆ cycloalkanes having from 1 to 2n halogen substituents such asfluorine, chlorine and/or bromine, where n is the number of carbonatoms; preferably C₁-C₂ alkanes having from 2 to 2n+2 fluorine and/orchlorine substituents), arenes (e.g., benzene), substituted arenes(e.g., N-methylpyrrole or C₆-C₁₀ arenes having from 1 to 8 halogensubstituents and/or C₁-C₄ alkyl and/or alkoxy substituents; preferablybenzenes having from 1 to 6 fluorine, chlorine, C₁-C₂ alkyl and/ormethoxy substituents), aliphatic ethers (e.g., ethers having two C₂-C₆branched or unbranched alkyl groups, or 1 methyl group and one C₄-C₆branched or unbranched alkyl group), cyclic ethers (e.g.,tetrahydrofuran or dioxane), and glycol ethers (e.g., of the formula(CH₃(CH₂)_(w))O((CH₂)_(x)O)_(y)(CH₂)_(z)CH₃), where x is independently2-4 [preferably 2], y is 1-4 [preferably 1 or 2], and w and z areindependently 0 to 3 [preferably 0]). Cycloalkanes (notably cyclooctane)appear to provide the best results with respect to ink stability.

The present ink may further comprise a surfactant (e.g., a surfacetension reducing agent, wetting agent, etc.), a binder and/or athickening agent, although no such additives are required. In fact, itis advantageous for the ink to exclude such additional components,particularly where such additional components include sufficiently highmolar proportions of elements such as carbon, oxygen, sulphur, nitrogen,halogens or heavy metals to adversely affect electrical properties ofthe resulting thin film. Thus, in one embodiment, the present inkincludes a small or trace amount of one or more high molecular weightsilanes (e.g., as described above), in an amount effective to improvethe wetting characteristics of the ink. Such higher molecular weightsilanes may be formed by the preferred method of making a hydrogenated(cyclo)silane. However, where they are present, each of these additionalcomponents may be present in trace amounts in the present inkcomposition. However, the surface tension reducing agent, which isconventional, may be present in an amount of from 0.01 wt. % to 1 wt. %,preferably 0.02 wt. % to 0.1 wt. % of the ink composition. In certainembodiments, the surface tension reducing agent may comprise aconventional hydrocarbon surfactant, a conventional fluorocarbonsurfactant or a mixture thereof. The wetting agent is generally presentin an amount of from 0.05 wt. % to 1 wt. %, preferably 0.1 wt. % to 0.5wt. % of the ink composition. The surfactant may be present in an amountof from 0.01 wt. % to 1 wt. %, preferably 0.05 wt. % to 0.5 wt. % of theink composition. The binder and/or thickening agent, each of which isconventional, may be present in an amount sufficient to provide the inkcomposition with predetermined flow properties at a given processingtemperature. However, typical amounts of these components in thecomposition are from 0.01 wt. % to 10 wt. %, preferably 0.1 wt. % to 5wt. %

Exemplary Methods of Forming a Semiconductor and/or Semiconducting ThinFilm

The present invention further concerns a method of forming asemiconductor and/or semiconducting thin film from the present(cyclo)silane compound(s), composition and/or ink. This method maycomprise the steps of depositing a layer of the (cyclo)silanecomposition compound(s), composition and/or ink on a substrate; andcuring the compound(s), composition and/or ink to form the semiconductorfilm. As discussed above, in general, the composition comprises orconsists essentially of the (cyclo)silane compound(s), and the inkcomprises the composition and a solvent in which the cyclic Group IVAcompound is soluble.

In this method, depositing may comprise spin coating, dip coating, spraycoating, ink jetting, slit coating, meniscus coating, or microspottingthe (cyclo)silane compound(s), composition or ink on the substrate.Also, curing may comprise oligomerizing and/or polymerizing the cyclicGroup IVA (cyclosilane) compound. Oligomerizing and/or polymerizing thecyclosilane generally comprises (i) heating the composition to atemperature of at least about 100° C. (preferably at least about 200° C.or at least about 300° C. to transform the cyclosilane into a highermolecular weight oligomeric, polymeric or [hydrogenated] elementalmaterial), (ii) irradiating the compound or composition, or (iii) bothheating and irradiating, as described in (i) and (ii). When curing isperformed at a relatively low temperature (e.g., from about 100° C. toabout 200° C., preferably from about 100° C. to about 150° C.), itgenerally evaporates or removes the solvent (particularly when performedunder vacuum), and may transform part or all of the cyclosilane into ahigher molecular weight oligomeric or polymeric material. Thus, curingmay comprise (i) a first heating phase at a first temperature toevaporate and/or remove any solvent, and (ii) a second heating phase ata second temperature higher than said first temperature to transform thecyclosilane into a polymeric or (hydrogenated) elemental material.Typically, curing times may vary from 10 seconds to 60 minutes(preferably 30 seconds to 30 minutes) depending on the appliedtemperature and the desired film characteristics (e.g., hydrogencontent, impurity level, density or extent of densification, level orpercentage of crystallinity, doping levels, doping profile, etc.).Furthermore, when an ink is deposited, curing may further comprisedrying the ink before heating and/or irradiating the compound orcomposition.

When the method of making a film includes irradiating the (cyclo)silanecompound(s) or composition, the method may further comprise patterningthe semiconductor thin film. In one embodiment, patterning comprisesselectively irradiating portions of the layer of (cyclo)silanecompound(s), composition or ink with light having a wavelength and/orintensity sufficient to oligomerize, polymerize or otherwise reduce thesolubility of the (cyclo)silane compound(s) in the irradiated portions,and subsequently removing non-irradiated portions of the layer with asuitable solvent to form the pattern (e.g., developing the layer). Thesubstep of selectively irradiating the layer may comprise (i)positioning at least one of the substrate and a mask such that theportions of the composition that will form the patterned structures canbe selectively irradiated, and the non-irradiated portions (i.e.,corresponding to the areas of the layer to be removed) cannot beirradiated, then (ii) irradiating the layer with light (e.g.,ultraviolet, visible or infrared light) through the mask. The mask,which is conventional, is generally one that absorbs light of awavelength or wavelength range used for the irradiating substep.Preferred UV radiation sources include those with an emission at 254 nm(e.g., a conventional handheld UV-lamp, an Hg lamp, etc.), as are knownin the art.

The curing step may comprise a “polysilane” formation phase or step, andan annealing phase or step. The term “polysilane” is used as aconvenient notation for any polymer of silane, germane, or combinationthereof. Conversion of the cyclic Group IVA compound(s) to form a dopedor undoped polysilane, polygermane, poly(germa)silane orpoly(sila)germane generally occurs by irradiation with an appropriatedose of an appropriate energy of radiation, or thermally at atemperature around or above 100° C. A conventional radical initiator,such as 2,2′-azobisisobutyronitrile (AIBN),1,1′-azobiscyclohexanecarbonnitrile, dibenzoylperoxide, butyl lithium,silyl potassium or hexamethyldisilane (and others) may lower thetemperature for polysilane formation to below 100° C. Other methods tocatalyze the formation of polysilanes from the cyclic Group IVAcompound(s) include adding known transition metal complexes such ascyclopentadienyl complexes of early transition metals such as Hf, Zr, Tiand V (and known derivatives thereof). The amount of radical initiatoradded can vary from 0.00001 mol % to 10 mol % with respect to the cyclicGroup IVA compound(s). Polysilanes may also be formed by ring openingpolymerization of cyclic silanes. Formation of the semiconductor filmgenerally occurs at a temperature above 200° C., more preferably above300° C., and most preferably from about 350° C. to about 400° C.

Preferred curing conditions for films formed from the present cyclicGroup IVA compound(s), composition or ink include curing at atemperature of about 400° C. or less, in the presence of a reducingatmosphere such as an argon/hydrogen mixture. Such conditions arebelieved to remove hydrogen and carbon-containing species from the filmeffectively and/or at a suitable rate. However, in such a case,subsequent lower-temperature annealing of a silicon film formed fromsuch cured compositions may dramatically improve the film's electricalcharacteristics. The lower-temperature annealing is generally conductedin a reducing atmosphere (preferably in an argon-hydrogen mixture, morepreferably containing ≦10% H₂ by weight or moles, and in oneimplementation, about 5 wt. % H₂), at a temperature in the range of from250° C. to 400° C., preferably from about 300° C. to about 350° C., fora length of time of from 10 minutes to 12 hours, preferably from about30 minutes to about 10 hours, and in one implementation, about 8 hours.

After curing and/or annealing, the method may further comprise cleaningthe substrate with the patterned semiconductor thin film thereon, forexample to remove any uncured composition or ink This step may compriserinsing with or immersing the substrate in a solvent, draining thesolvent from the substrate, and drying the substrate and patternedsemiconductor thin film Solvent rinsing or washing may include the sameprocedure(s) as are typically used in photoresist development and/orphotoresist etching (e.g., rinsing, immersing, spraying, vaporcondensation, etc.). Preferred solvents include solvents in which theunpolymerized cyclic Group IVA compounds have a high solubility, such asthe hydrocarbon and ether solvents described above for the exemplary ink

In preferred embodiments, the pattern comprises a two-dimensional arrayof lines having a width of from 100 nm to 100 μm, preferably from 0.5 μmto 50 μm, and more preferably from 1 μm to 20 μm. The lines may have aninter-line spacing of from 100 nm to 100 μm, preferably 200 nm to 50 μm,more preferably 500 nm to 10 μm. Furthermore, at least a subset of thelines may have a length of from 1 μm to 5000 μm, preferably 2 μm to 2000μm, more preferably 5 μm to 1000 μm, and a thickness of from 0.001 μm to1000 μm, preferably 0.01 μm to 500 μm, more preferably 0.05 μm to 250μm. Furthermore, the lines may comprise a first set of parallel linesalong a first axis, and a second set of parallel lines along a secondaxis perpendicular to the first axis. Although parallel andperpendicular lines may minimize adverse effects from adjacent linesand/or maximize the predictability of electromagnetic field effects fromadjacent lines, the patterned lines may take any shape and/or take anycourse that can be designed and formed.

Exemplary Semiconducting Thin Film Structures

A further aspect of the invention relates to a semiconducting thin filmstructure comprising or consisting essentially of a partiallyhydrogenated, at least partially amorphous Group IVA element, the GroupIVA element comprising at least one of silicon and germanium, thesemiconducting material having less than 100 ppm (preferably less than10 ppm, more preferably less than 1 ppm) of Group IIIA metalcontaminants (other than intentionally added boron) relative to theGroup IVA element. In many cases, the semiconducting thin film structurecomprises a pattern of semiconducting material on a substrate. Thesemiconducting material in the present semiconducting thin filmstructure is preferably made from the present composition and/oraccording to the present method(s). The cyclic Group IVA compound(s) inthe present composition may help improve the quality of the thin filminterface to adjacent oxide, for example by improving planarization ofthe semiconductor thin film. Improved adherence to an underlyingsubstrate may also be provided, possibly by increasing the surface areaof the film that makes chemical and/or physical contact with theunderlying substrate at or before the time of curing and/or annealing.

In the present thin film structure, the at least partially hydrogenatedamorphous Group IVA element preferably comprises amorphous silicon.Also, the (partially) hydrogenated, amorphous Group IVA element mayfurther comprise a dopant (e.g., B, P or As), which may be covalentlybound to Group IVA atoms therein (see, e.g., copending and commonlyassigned U.S. Ser. No. 10/616,147, filed on Jul. 8, 2003, the relevantportions of which are incorporated herein by reference). In such a case,the dopant concentration profile or gradient may be substantiallyuniform throughout the entire thickness of the semiconductor thin film.

In another embodiment, the cured thin film may have a controlled dopingprofile; for example, it may comprise multiple layers of differentlydoped silicon. In one embodiment, a bottom layer may comprise one ofp-doped silicon (i.e., where the composition comprises a compoundcontaining boron) or n-doped silicon (i.e., where the compositioncomprises a compound containing P or As), a second layer thereon maycomprise the other of p-doped silicon or n-doped silicon, an optionalthird layer on the second layer that comprises silicon having the samedopant type (p-doped or n-doped) as the bottom layer, in which thedopant may be present in the same, a higher or a lower concentrationthan the bottom layer, an optional fourth layer on the third layer thatcomprises silicon having the same dopant type (p-doped or n-doped) asthe second layer, in which the dopant may be present in the same, ahigher or a lower concentration than the second layer, and so on.Alternatively, the cured thin film may comprise lightly doped silicon(i.e., where the composition comprises a compound containing B, P or Asin an amount or percentage by weight or moles sufficient to provide,e.g., from 10⁻¹⁰ to 10⁻⁷ moles of dopant per mole of Group IVA element)and a layer or region of heavily doped silicon (e.g., where thecomposition comprises a compound containing B, P or As in an amount orpercentage by weight or moles sufficient to provide, e.g., from 10⁻⁷ to10⁻⁴ moles of dopant per mole of Group IVA element) of the same dopanttype. Such a structure may further comprise (i) a layer or region ofoppositely doped silicon above it, below it and/or adjacent to it,and/or (ii) a layer or region of very heavily doped silicon (e.g., wherethe composition comprises a compound containing B, P or As in an amountor percentage by weight or moles sufficient to provide, e.g., from 10⁻⁴to 10⁻³ moles of dopant per mole of silicon) above it and/or adjacent toit.

In a further embodiment, the semiconducting thin film may comprise oneor more layers in a thin film transistor (TFT) and/or capacitor (such asa MOS capacitor). In yet another embodiment, the semiconducting thinfilm may be used for a photovoltaic device. For instance, a photovoltaicdevice may be made by the above process, but with a film thickness offrom 1 to 1000 microns, preferably 5 to 500 microns, whereas thepreferred thickness for a TFT is from 10 to 500 nm, more preferably from50 to 100 nm.

However, in a preferred embodiment, the present thin film structurecomprises a patterned, two-dimensional array of lines, each line havinga width of from 100 nm to 100 μm, more preferably from 0.5 μm to 50 μm,and even more preferably from 1 μm to 20 μm. The lines may have aninter-line spacing of from 100 nm to 100 μm, preferably from 0.5 μm to50 μm, more preferably from 1 μm to 20 μm. The thin film pattern linesmay also have a length of from 1 μm to 5000 μm, at least a subset of thelines preferably having a length of from 2 μm to 1000 μm, morepreferably from 5 μm to 500 μm. The lines may have a thickness of from0.001 μm to 1000 μm, preferably from 0.005 μm to 500 μm, more preferablyfrom 0.05 μm to 100 μm.

In certain embodiments, the substrate may comprise a transparent glassor plastic display window, and the circuit, circuit element, integratedcircuit or block thereof may comprise a thin film transistor (TFT)display element. Alternatively, the substrate may comprise a siliconwafer or metal substrate, and the circuit, circuit element, integratedcircuit or block thereof may comprise a radio frequency identificationcircuit (e.g., a so-called RF ID tag or device).

EXAMPLES Synthesis of Perphenylcyclosilanes

In a 3 L four neck round bottom flask fitted with an addition funnel, areflux condenser, a thermocouple and an overhead stirrer, 18.3 g (2.64mol) Li ribbon (Aldrich, 0.38 mm thick) cut into small pieces underargon are suspended in 1 L of dry THF (tetrahydrofuran). Under vigorousstirring, 333 g (1.32 mol) Ph₂SiCl₂ (Aldrich) is added to thissuspension at a rate that allows for complete addition after 60 to 80minutes. The suspension is kept between −5° C. and 5° C. duringaddition. After addition is complete, the reaction solution is allowedto warm up to room temperature. Additional stirring for a minimum of 3hrs, or until all lithium has reacted, produces a yellow to red coloredsuspension. The suspension is heated to reflux for 3 hrs. After coolingto room temperature, any remaining silyllithium compounds are destroyedby adding a small amount (2-10 mL) of deionized water. The resultingwhite suspension (which can be handled in ambient atmosphere) is pouredonto 4 L of deionized water and stirred vigorously for 3 hours. The offwhite precipitate is filtered and washed with 5×200 mL of DI waterfollowed by 5×200 mL of cyclohexane. The resulting colorless powder isdried under vacuum at 180° C. for 24 hours. The yield after drying is200 g.

A thermogravimetric analysis of the powder indicated no mass loss whenheated to 200° C. ¹H-NMR analysis showed that the powder is a mixturecontaining at least 4 different species. The relative amounts observedfor each species may vary from batch to batch. Generally, the reactionproducts include 60-98 mol % (Ph₂Si)₅, 1-40 mol % (Ph₂Si)₄ and 0.5-10mol % for other species, including (Ph₂Si)₆. The components of themixture may be separated by recrystallization from toluene or ethylacetate, whereby both (Ph₂Si)₅ and (Ph₂Si)₄ have been isolated in >99%purity as determined by ¹H-NMR. The identity of both (Ph₂Si)₅ and(Ph₂Si)₄ have been verified by X-ray structure determination and meltingpoint determination.

Larger Scale Synthesis of Perphenylcyclosilanes

In a 12 L four neck round bottom flask fitted with an addition funnel, areflux condenser, a thermocouple and an overhead stirrer, 73.6 g (10.6mol) Li ribbon (Aldrich, 0.38 mm thick) cut into small pieces underargon, is suspended in 4 L of dry THF (tetrahydrofuran). Under vigorousstirring, 1.338 kg (5.284 mol) Ph₂SiCl₂ (Aldrich) is added to thesuspension at a rate that allows for complete addition after 210minutes. The suspension is kept between −5° C. and 5° C. duringaddition. After addition is complete, the reaction solution is allowedto warm up to room temperature. Additional stirring for a minimum of 3hrs, or until all lithium has reacted, produces a yellow to red coloredsuspension. The suspension is heated to reflux for 7 hrs. After coolingto room temperature, any remaining silyllithium compounds are destroyedby adding a small amount (10-20 mL) of deionized water. The resultingwhite suspension (which can be handled in ambient atmosphere) is pouredinto 20 L of deionized water and stirred vigorously for 3 hours. The offwhite precipitate is filtered and washed with 3×1000 mL of DI waterfollowed by 3×500 mL of cyclohexane. The resulting colorless powder isdried under vacuum at 170° C. for 24 hours. The yield after drying is760 g.

A thermogravimetric analysis of the powder indicated no mass loss whenheated to 200° C. ¹H-NMR analysis showed that the powder is a mixturecontaining at least 4 different species (see Table 1). In one example,the mixture contained 72 mol % (Ph₂Si)₅, 25 mol % (Ph₂Si)₄, and 3 mol %of other species, including (Ph₂Si)₆. Data from other examples are shownin Table 1. The mixture may be separated by recrystallization fromtoluene or ethyl acetate, whereby (Ph₂Si)₅ has been isolated in >95%purity as determined by ¹H-NMR. The identities of both (Ph₂Si)₅ and(Ph₂Si)₄ have been verified by melting point determination.

TABLE 1 Other Phenylsilane Yield Amount [Ph₂Si]₅ [Ph₂Si]₄ speciesincluding (%, based on Example (g) (%) (%) [Ph₂Si]₆ (%) [Ph₂Si]_(x), x =4.5) 1 142 70 27 4 76 2 188 64 32 4 78 3 118 90 5 5 71 4 203 90 5 5 85 5200 71 24 5 83 6 197 70 26 5 82 7 207 86 8 6 86 8 99 85 9 6 82 9 204 859 6 85 10 203 92 3 5 85 11 203 84 7 9 84 12 760 73 22 5 79

Synthesis of Cyclosilanes

In a 3 L 3-neck flask equipped with a reflux condenser and a gasdispersion tube, 100 g of a perphenylcyclosilane mixture obtained asdescribed above and 3 g freshly sublimed A1Cl₃ are suspended in 1 L ofdry cyclohexane. Under vigorous stirring, dry HCl gas is bubbled throughthis suspension at ambient temperature until an almost colorless toyellow solution is obtained. Under continuous HCl addition, the solutionis stirred for another 5-8 hrs or until all phenyl groups have beenreplaced by chlorine as indicated by ¹H-NMR, ²⁹Si-NMR and FT-IR. 400 mLof a 1M ethereal solution of LiAlH₄ (Aldrich) is added under vigorousstirring to the perchlorocyclosilane solution at 0° C. After 1 hour, theaddition is complete, and the resulting suspension is further stirred atroom temperature for another 15 hrs. Two phases are formed upon removing800 ml solvent under reduced pressure. The lower phase containingprecipitated byproduct is removed with a separatory funnel to yieldabout 125 ml of a clear solution. The reaction product is distilledunder reduced pressure (0.5 Ton, 25° C.) to afford 9 ml clear colorlessliquid.

¹H-NMR, ²⁹Si—NMR, GC/MS, GPC/UV and GPC/RI analysis of the liquidconfirm that a mixture of (cyclo)silanes has been formed withcyclopentasilane as the main component (between 75 and 99 mol %).Cyclohexasilane can be identified as a second component (between 0.5 and10 mol %). Other silane species are formed in amounts between 0 and 6mol %, as well as aromatic and aliphatic byproducts. Table 2 below listsproduct distribution data in wt. % (as determined by GC/MS) from anumber of examples of cyclosilane synthesis performed according to thisdescription. The numbers may not add up to 100% in all cases due torounding.

TABLE 2 Si_(n)H_(2n−x) [H₂Si]_(x) Si_(n)H_(2n+2) n > 4, Or- Ex- Amount[H₂Si]₅ [H₂Si]₆ x > 6 4 n 8 x > 0 ganics ample (g) (%) (%) (%) (%) (%)(%) 13 3.0 78.8 8.6 0.3 5.0 0.2 7.2 14 6.0 88.3 4.7 0.0 1.4 0.2 5.3 154.0 91.1 5.8 0.0 1.3 0.0 5.3 16 1.9 90.4 7.0 0.3 0.8 0.7 0.9 17 7.9 91.47.2 0.2 0.5 0.0 0.7 18 3.8 83.8 10.0 0.5 1.3 0.2 4.2 19 2.3 99.4 0.6 0.00.0 0.0 0.0 20 7.2 92.1 5.2 0.2 0.7 0.9 0.9 21 7.3 85.5 9.7 1.0 1.1 0.52.2 22 9.5 92.3 6.4 0.1 0.7 0.2 0.3

Water Wash

1 mL of a cyclosilane mixture as described above was added to an ambervial containing 2 ml degassed, deionized (DI) water. The two phases weremixed vigorously and allowed to sit for 1 min. The upper phase (whichcontained the cyclosilane) was then transferred to another vial, driedover 4 {acute over (Å)} molecular sieves and filtered through a 0.2 μmmembrane to obtain a clear liquid.

Treating the cyclosilane mixture with water after distillation of theraw material effects a substantial reduction of the amount of Al in thesilane and substantially removes Al contamination in the Si film afterspin coating. The amount of Al in the silane mixture before treatingwith water may be as high as 2%, depending on the nature and amount ofAl byproduct (following the reduction of the perchlorocyclosilanemixture and the distillation procedure used to purify the reducedcyclosilane mixture). Regardless of the absolute amount of Al beforecontact with water, water washing and the subsequent separation of thesilane phase from the water phase that now contains the Al componentresults in a silane film after spin coating in which the Al content isreduced to less than 100 ppm, preferably less than 10 ppm and morepreferably less than 1 ppm. The treatment with water may also be carriedout with slightly acidified water (e.g., water containing bufferedacetic acid to keep the pH below 7). Exposure of the silane mixture toalkaline conditions should be avoided as it may lead to uncontrolledSi—Si bond scission and polymerization. Minimal chemical effects on thesilane composition may be achieved when aqueous washing is carried out(preferably with neutral or DI water). It has been found that continuedor longer exposure of the cyclosilane mixture to water may lead toisomerization of some silanes to different silanes, including highermolecular weight silanes. This effect may be advantageously used toadjust the volatility and/or viscosity of the silane composition in anink before deposition. For example, viscosity, surface tension andwetting behavior of the resulting silane composition/film may beadjusted in this way. Contact with water can occur by either adding thesilane mixture to water or adding the water to the silane mixture. Theratio of water to silane mixture is in the range of 10:1 to 1:10, morepreferably between 5:1 and 1:5, and even more preferably it is about2:1. The silane mixture after separation from the aqueous phase isfurther dried using standard drying methods, such as contacting withmolecular sieves. Preferably, the molecular sieves comprise beads of the4{acute over (Å)} type (e.g., commercially available from AldrichChemical Co.). After filtering, as the cyclosilane is generallytemperature and light sensitive, so it is stored at low temperatures,preferably at or below room temperature and with light and UV protection(e.g., storing in a darkened vial or wrapping with aluminum foil) tofurther avoid any unwanted isomerization or generation of highermolecular weight components.

CONCLUSION/SUMMARY

Thus, the present invention provides a method for making a(cyclo)silane, a silane composition having reduced metal impurities, anink including the silane composition, and a method for makingsemiconductor structures and/or semiconducting thin films. By washingthe (cyclo)silane with a polar-phase washing composition or agent, asubstantial amount of certain metal impurities (e.g., aluminum and/oralkali metals, such as lithium or sodium) may be removed, therebygreatly improving the electrical properties of a thin film formed from acomposition containing the (cyclo)silane.

The foregoing descriptions of specific embodiments of the presentinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical application,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the Claims appended hereto and theirequivalents.

What is claimed is:
 1. A method of making a film comprising siliconand/or germanium, comprising: a) printing or coating an ink on asubstrate, the ink comprising: i) a silane consisting essentially of (i)Si and/or Ge atoms and (ii) hydrogen atoms, the ink having less than 100parts of a water soluble metal impurity per million atoms of Si or Ge inthe film; and ii) a solvent in which the silane is soluble; and b)drying the ink to form said film.
 2. The method of claim 1, wherein theink is printed in a pattern on the substrate.
 3. The method of claim 1,wherein the ink is coated in a continuous film on the substrate.
 4. Themethod of claim 1, wherein the water soluble metal impurity comprisesaluminum, lithium, sodium, potassium, rubidium, or cesium.
 5. The methodof claim 1, further comprising heating and/or irradiating the compoundor composition to form a silicon-containing thin film.
 6. The method ofclaim 5, wherein the silicon- and/or germanium-containing film containsless than 10 parts water soluble metal impurity per million atoms of Sior Ge.
 7. The method of claim 6, wherein the silicon-containing filmcontains less than 1 parts water-soluble metal impurity per millionatoms of Si or Ge.
 8. The method of claim 1, further comprising curingthe printed or coated ink to form a cured silicon-containing film. 9.The method of claim 1, further comprising irradiating the printed orcoated ink under conditions sufficient to form a doped or undopedpolysilane, polygermane or germanium-substituted polysilane having amolecular weight sufficiently high and/or a chemical compositionsufficiently insoluble to resist subsequent treatment with processingsolvents.
 10. The method of claim 1, further comprising (i) heating thecomposition to a temperature of at least about 300° C. to transform thesilane into a higher molecular weight oligomeric, polymeric orhydrogenated elemental material, (ii) irradiating the silane, or (iii)both (i) and (ii).
 11. The method of claim 1, comprising inkjetting ormicrospotting the ink on the substrate.
 12. The method of claim 1,comprising spin coating, dip coating, spray coating, slit coating ormeniscus coating the ink on the substrate.
 13. The method of claim 1,wherein the silane is present in the ink in a percentage by volume offrom 0.1 to 50 vol. %.
 14. The method of claim 13, wherein the silane ispresent in the ink in a percentage by volume of from 1.0 to 20 vol. %.15. The method of claim 1, wherein the silane comprises one or morecompounds of the formula A_(x)H_(y), where each A is independently Si orGe, and x and y are selected such that the silane is liquid at atemperature from 15° C. to 30° C.
 16. The method of claim 1, wherein theink further comprises one or more high molecular weight silanes having60 or more silicon atoms therein.
 17. The method of claim 16, whereinthe ink contains the one or more high molecular weight silanes in anamount effective to improve wetting characteristics of the ink.
 18. Themethod of claim 12, comprising spin coating the ink on the substrate.19. The method of claim 12, comprising slit coating the ink on thesubstrate.
 20. The method of claim 12, comprising dip coating ormeniscus coating the ink on the substrate.